Acoustic sensing tools are generally known in hydrocarbon production applications for detecting acoustic activity in formations. Acoustic activity, which includes seismic or microseismic activity, may occur in a formation either passively or as a result of active stimulation. Passive acoustic activity can occur during production as fluid is removed from the formation. During active stimulation, on the other hand, acoustic activity may be induced by any of several known methods. In hydrofracture monitoring, for example, a fracture fluid is injected into the formation to stimulate microseismic activity. Alternatively, a seismic generator may be deployed at the surface or below the surface (such as in the production wellbore or in a separate wellbore) to generate the microseismic activity.
Regardless of how the acoustic activity occurs, acoustic sensing tools may be used to detect information related to the acoustic activity. That information may then be used to understand the characteristics of the fracture (propagation direction, geometry, and dip, among other parameters). During active stimulation applications, the information may further be used to adjust, in real time, the seismic generation parameters in case of a mismatch between the planned and actual fracture. The “real-time” expression refers here to enabling a reaction in a time which is fast enough to have an impact on the economics of the fracturing job (for instance stopping seismic generation where the fracture appears to be in danger of extending into a water zone).
Various acoustic sensing tools (or “sondes”) are known for use downhole. These tools may be deployed via a wireline or similar means, or may be attached to production tubing as it is installed into a wellbore. When deployed by tubing, for example, the acoustic sensing tool must be capable of moving from a retracted position, which permits movement along the wellbore, to an expanded position, in which the acoustic sensing tool engages a surface of the wellbore to facilitate acoustic coupling between the sensor and the formation. Many conventional sensor tools are permanent installations once deployed, and therefore cannot be repositioned or retrieved after use. Other tools purport to be retrievable, but such retrieval requires dragging the acoustic sensing tool along the wellbore in the expanded position, or is otherwise overly difficult.